1. Field of the Invention
The present invention relates to an image filter circuit for generating unsharp image signals used to subject image signals to dodging treatment in an image processing apparatus for image processing the image signals.
2. Description of the Related Art
At present, an image recorded on a photographic film such as a negative film, a reversal film and the like (hereinafter referred to as a film) is printed to a photosensitive material such as a photographic paper and the like by so-called direct exposure in which the photosensitive material is subjected to areal exposure by being projected with an image recorded on a film.
Recently, research of printers making use of digital exposure, that is, digital photo printers has been carried out. In the digital photo printers, after image information which has been recorded on a film is photoelectrically read out, the read-out image information is converted as image signals to be recorded by being subjected to various kinds of digital image processing. Then, a photosensitive material is scanned with and exposed to recording light which has been modulated in accordance with the image signals to thereby record an image (a latent image) and the recorded image is developed, thus, the photographic print is obtained.
Basically, the digital photo printers are composed of an image reading apparatus for photoelectrically reading out an image recorded on a film, an image processing (setup) apparatus for subjecting a read-out image to image processing and determining exposure conditions for recording the image, an image recording apparatus for scanning and exposing a photosensitive material in accordance with the thus determined exposure conditions and developing the image and the like.
In the image reading apparatus used in the digital photo printers, reading light produced by a light source impinges upon a film to thereby obtain projected light which carries an image recorded on the film. The image carried by the projected light is formed to an image sensor such as a CCD sensor or the like through an image forming lens, and is read out by subjecting the projected light to photoelectrical conversion in the image sensor. Then, after the thus read image is subjected to various kinds of image processing when necessary, the image is input to the image processing apparatus as the image signals corresponding to the image recorded on a film.
The image processing apparatus sets image processing conditions in accordance with image signals having been input from the image reading apparatus and displays an image in accordance with the image signal on a display apparatus such as a display. After the operator carries out testing and adjusts the image processing conditions when necessary, the image signals are subjected to a desired image processing and are input to the image recording apparatus as output image signals (exposure conditions) for recording the image.
In the image recording apparatus, when it is, for example, an apparatus making use of a light beam scanning exposure, light beams are modulated in accordance with the image signals input from the image processing apparatus and deflected in a main scanning direction. Also, the photosensitive material is conveyed in an auxiliary scanning direction, which is approximately normal to the main scanning direction. In this manner, the photosensitive material is exposed to the light beams to thereby form a latent image. The photosensitive material is then subjected to development processing in accordance with the photosensitive material. A finished print (photograph) on which the image recorded on a film is reproduced is thereby obtained.
In the digital photo printers, since a film is photoelectrically read and exposure conditions are determined after a color/density correction is carried out by signal processing, a period of time during which a single image is exposed is short and the exposure time is fixed to respective values in accordance with an image size. As a result, printing can be promptly carried out as compared with the conventional areal exposure. Editing such as combining of a plurality of images, division of an image, and the like, and image processing such as color/density adjustment and the like, can be carried out freely. Therefore, finished prints having been edited and processed freely in accordance with their use can be output.
Since the images recorded on finished prints can be stored in a recording medium such as a floppy disk and the like as image information, it is not necessary to prepare a film serving as an original image when prints are made additionally. Further, since it is not necessary to determine exposure conditions again, a job can be promptly and simply carried out. In the prints made by the conventional direct exposure, the images recorded on a film or the like cannot be perfectly reproduced in some points such as resolution, color/density reproducibility and the like. However, with the digital photo printers, prints, on which the images (image density information) recorded on a film or the like are reproduced approximately perfectly, can be output.
Incidentally, recording conditions under which an image is recorded on a film are not fixed and there are many cases where a large amount of difference exists between a bright portion and a dark portion as found in an image recorded using an electronic flash, a backlighted scene and the like. When such a film image is exposed by a conventional method and made to a finished print, there is a tendency that details become imperceptible due to insufficient gradation in either one of a bright portion and a dark portion on the print. For example, in cases where a picture of a person is recorded against the light, if the picture is exposed such that the image of a person may be preferably clear, the bright portion, such as a sky region, will become white and its details will become imperceptible. Whereas, if the picture is printed such that the bright portion, such as the sky region, may become preferably clear, the image of the person will become black and its details will become imperceptible.
Therefore, when a photosensitive material is exposed using a film image having a large difference between a bright portion and a dark portion as an original image, there have heretofore been employed a so-called dodging treatment.
The dodging treatment is a method of obtaining a finished print in which a proper image is reproduced over an entire picture in such a manner that an ordinary level of exposure is carried out to a portion having an intermediate image density, an amount of exposure light is increased to a portion where an image tends to become white (a bright portion) and an amount of exposure light is reduced to a portion where an image tends to become black (a dark portion) to thereby correct a very bright portion and a very dark portion of the image recorded on film.
Conventional apparatuses using the areal exposure employs the dodging treatment to locally modify an amount of exposure light in accordance with an image recorded on a film. More specifically, the dodging treatment uses a method of carrying out exposure by inserting a blocking plate, an ND filter or the like into an exposure light passage, a method of locally changing an amount of light produced by an exposure light source, a method of creating monochrome films by reversing the bright portion and the dark portion of an image recorded on film and carrying out exposure by superimposing the films, and the like.
Digital photo printers intend to obtain an effect, which is similar to that obtained by dodging treatment or dodging processing which uses an areal exposure, by subjecting image signals to image processing. This image processing is carried out in such a manner, for example, that the image density of the portion where an image tends to become white is increased, whereas the image density of the portion where the image tends to become black is decreased so that the contrasts in the respective regions of the portion where the image tends to become white and the portion where the image tends to become black are emphasized as well as the contrast of an entire image is adjusted.
The above image processing is carried out such that the image signals are filtered using, for example, a filter to thereby generate unsharp image signals used to carry out dodging treatment. At the time, it is necessary to use a filter large enough to carry out calculation treatment to image signals which cover, for example, 100 pixels×100 pixels to obtain the effect similar to that obtained by the dodging treatment which uses the areal exposure. Thus, a problem arises in that an image filter circuit for carrying out filter treatment is increased in size.